Can we deprecate `--proxy-to-worker` / `-sPROXY_TO_WORKER`?

[sbc100]

I don't think they are going to be many folks using this.

IIUC it was mostly and experiment from the early days of emscripten to try to get synchronous applications running in a worker. However, since it always takes over the whole browser window I can't imagine many folks actually using it.

[sbc100]

See #25439

[juj]

The use case of proxying to Worker itself is sound, because just enabling multithreaded programs require nonstandard HTTP server configuration.

So applications that are based on async message passing multiprocessing-style of communication could definitely utilize proxying to Worker.

It is just that the current implementation of --proxy-to-worker is monolithic, which makes it a bit dusty to keep up with the times.

[sbc100]

I think we should only consider keeping it around if there are active users of the feature. If there are none, I don't see any point in maintaining it and continuing to fix bugs in it.